I have a mid '70s MC that I am trying to get up and running after 3 years of mostly sitting. I have a Holley 600cfm 4bbl on order to replace the auto-version that it had when I bought it. (I feel fortunate because I used it for quite some time before I knew about j-tubes, and the potential danger.) I have attached a photo of the motor.

My question is about the exhaust. The pipes exit the manifolds and then go through the floor on the outside of the stringers. The pipes are both kinked a little where they turn to go through the floor. Is this normal? Also, the pipes vibrate and shake when the motor is running. My mechanic friend fears that this means the inner lining has separated and could restrict the flow.

One of the 3" pipes sprung a leak many years ago. Since I was on vacation at the time, I applied copious amounts of RTV silicone, and then wrapped it with duct tape - of course with the intention of fixing it properly later. Well, the fix really worked for many years.

Now, there is again a small leak. How do I go about replacing the exhaust pipes? Can I pull them through from the outside of the transom (of course, pulling the new one along with it)?

Thrall

08-26-2009, 05:47 PM

Just saw a thread on this a week ago or so. Yeah, basically, take off the exhaust outlets/flappers and pull teh old hose (and muffler?) out. Fish a new one in.

thatsmrmastercraft

08-27-2009, 02:10 AM

I have a mid '70s MC that I am trying to get up and running after 3 years of mostly sitting. I have a Holley 600cfm 4bbl on order to replace the auto-version that it had when I bought it. (I feel fortunate because I used it for quite some time before I knew about j-tubes, and the potential danger.) I have attached a photo of the motor.

My question is about the exhaust. The pipes exit the manifolds and then go through the floor on the outside of the stringers. The pipes are both kinked a little where they turn to go through the floor. Is this normal? Also, the pipes vibrate and shake when the motor is running. My mechanic friend fears that this means the inner lining has separated and could restrict the flow.

One of the 3" pipes sprung a leak many years ago. Since I was on vacation at the time, I applied copious amounts of RTV silicone, and then wrapped it with duct tape - of course with the intention of fixing it properly later. Well, the fix really worked for many years.

Now, there is again a small leak. How do I go about replacing the exhaust pipes? Can I pull them through from the outside of the transom (of course, pulling the new one along with it)?

Looking at the exhaust manifold design that you have, this must be a '77 or older boat. The 77's had mufflers, but previous boats had exhaust pipes. Not sure where you would come up with the pipe, but skidim carries the mufflers for '77 and later boats. Perhaps installing mufflers is the simple answer?

pasmadj

08-27-2009, 08:47 AM

Looking at the exhaust manifold design that you have, this must be a '77 or older boat. The 77's had mufflers, but previous boats had exhaust pipes. Not sure where you would come up with the pipe, but skidim carries the mufflers for '77 and later boats. Perhaps installing mufflers is the simple answer?

I think I would really prefer to install mufflers. When my exhaust ports clear the water, wow. All conversation in the boat gets difficult.

I have heard that engines are designed to operate with a certain amount of back pressure. If I put in mufflers, will that screw something up? Will the engine not run correctly?

pasmadj

08-27-2009, 08:51 AM

Does anyone know about the vibrating exhaust pipes? Is that normal, or is the pipe failing in some way?

pasmadj

08-27-2009, 08:52 AM

Does anyone know anything about the kinking of the pipes as they turn to go through the floor? Do I need to post some better photos?

TMCNo1

08-27-2009, 09:38 AM

Since your considering replacing the exhaust hose this may be your best bet, http://www.skidim.com/prodinfo.asp?number=MPI252-3000, just discuss your situation with them before ordering any.

thatsmrmastercraft

08-27-2009, 10:07 AM

You will most likely need to go to smaller jets in the carb to lean things out a little once you put on the mufflers. The guys at skidim should have some insight into whats needed. If not, there are plenty of us on this site who can walk you through re-jetting.

pasmadj

08-30-2009, 11:23 PM

The pipes are flattened out as they turn to go through the floor. They also vibrate when the engine is running. Is this normal, or is due to failing pipes?

thatsmrmastercraft

08-30-2009, 11:27 PM

That hose looks way too restricted where it goes through the floor. I bet it is the hose without the interior wire to keep it from binding. You probably need to replace it with hose with the wire available from skidim.